1. Field of the Invention
The present invention is concerned with novel phenyl isothiocyanates their method of manufacture as well as liquid crystalline mixtures and electro-optical devices containing same.
2. Background Description
Liquid crystals have recently gained considerable importance as dielectrics in indicating devices, since the optical properties of such substances can be influenced by an applied voltage. Electro-optical devices based on liquid crystals are well known to the person skilled in the art and can be based on various effects such as, for example, the dynamic scattering, the deformation of aligned phases (DAP type) the Schadt-Helfrich effect (rotation cell), the guest/host effect or a cholesteric-nematic phase transition (phase change effect).
Liquid crystals must, however, satisfy a number of requirements in order to be suitable as dielectrics for electro-optical indicating devices. For example, they must have a good chemical stability towards environmental factors such as e.g. heat, moisture, air electromagnetic radiation in the infra-red, visible and ultra-violet region. Further, they should be colourless, should have short response times and not too high a viscosity, should give a good contrast and should have a nematic or cholesteric mesophase in all temperature ranges in which the liquid crystal cell is to be operated. Other properties must fulfill different conditions depending on the type of cell which is used, for example liquid crystals which are used in rotation cells should have a large positive anisotropy of the dielectric constants (.DELTA..epsilon.=.epsilon..sub..parallel. -.epsilon..sub..perp. &gt;0, .epsilon..sub..parallel. signifying the dielectric constant along the longitudinal axis of the molecule and .epsilon..sub..perp. signifying the dielectric constant perpendicular thereto) and liquid crystals which are used in guest/host cells should have a large positive or negative anisotropy of the dielectric constants. Moreover, in both cases a low threshold potential and a conductivity which is as small as possible are desirable.
Since, in general, it is not possible to achieve all desired and to some extent conflicting properties with a single compound, attempts have mainly been made to optimize the properties for the particular applications by mixing several components. In this case it is, however, important that the components undergo no chemical reactions with one another and have a good miscibility with one another. Further, the mixtures formed should have no smectic mesophases, at least at temperatures at which the liquid crystal cells are to be operated.